LONDON (AFP) - Roger Federer said on Friday (Nov 9) he is focused on winning the ATP Finals for a seventh time rather than the 100th singles title of his glittering career as he looks to end 2018 in style.

The Swiss 20-time Grand Slam champion is playing in the season-ending finale for a 16th time and has tasted victory on a record six occasions - twice in London, twice at Shanghai and twice in Houston.

The world number three has won four titles this year, including a second consecutive Australian Open, and stands on 99 career singles titles - second only to retired American Jimmy Connors, who amassed 109.

"I don't think it matters really where I win my 100th as long as it's going to happen at one point," said the 37-year-old, who has not won the ATP Finals since 2011.

"That's going to be exciting. I think if I won here it's more about winning the World Tour Finals and not about winning my 100th.

"I love playing this event. I always have, ever since I qualified for the very first time back in 2002. That was a massive highlight in my career to be among the best eight and I actually had a great run too, that very first time in Shanghai."

Federer, who plays Japan's Kei Nishikori in his tournament opener at London's O2 arena on Sunday, said overall he is happy with his season.

"Maybe Wimbledon and the US Open didn't go the way I was hoping but those were really the only two disappointments of the season," he said.

"I won a bunch of tournaments again, played great at the Australian Open.

"I've just had a really solid season and I stayed injury-free also in particular for most of the year so I'm actually very happy with this season so far," he added.

"I've got one more left so hope I don't go on vacation with three losses." The veteran said he does not find age a factor in terms of sustaining form and fitness right through to the end of the season.

"It's really only Novak (Djokovic) who can say at this point 'If I play as well as I have done the last few months maybe I can also win the World Tour Finals' but not even that is a given because, especially in the best-of-three-set matches indoors, margins are slimmer so you can slip fast.

"I've played well since 2011 even though I didn't end up winning the World Tour Finals any more but I feel like I've done well and it doesn't feel like it's that long ago. I just feel like there was always a couple of guys maybe just a little bit better during that week."